1. Field of the Invention
The present invention relates to an image reading system for reading an original image in, e.g., an image scanner, a facsimile apparatus, and the like and, more particularly, to an image reading system suitably used in an original reading apparatus which illuminates an original using a linear light source comprising an LED (light-emitting diode) array and senses the linear image using a CCD (charge coupled device) one-dimensional image sensor.
2. Related Background Art
As a conventional image reading apparatus used in, e.g., a scanner, a facsimile apparatus, and the like, an apparatus using a reduction optical system, as shown in FIG. 12, is known.
This apparatus comprises a light source 55 which extends in the longitudinal direction to illuminate an original 56, a mirror 54 for bending the optical path to make the entire apparatus compact, a lens 52 for imaging original information light, a correction plate (shading plate) 53 for correcting the lens cosine rule of the white output waveform, and a line CCD image sensing element (to be referred to as a CCD hereinafter) 51 for converting optical information into an electrical signal. The apparatus also comprises an IC (not shown) comprising, e.g., an A/D converter for A/D converting an image signal output from the CCD 51 before the image signal is transferred to an image processing system, and the like.
Such image reading apparatus normally uses an inexpensive Xenon (Xe) lamp, an LED, or the like as the light source to attain a cost reduction of the apparatus.
However, in the conventional apparatus, since the Xe lamp, LED, or the like serving as the light source has a small absolute light amount, the accumulation time for reading of the CCD must be prolonged or the sensitivity of a light-receiving unit must be increased so as to obtain stable image information. Under the circumstances, although development associated with high-speed driving of CCD devices is underway, the light-receiving unit of the CCD for photoelectrically converting optical information of an original has limited sensitivity characteristics, and the original must be irradiated with light in a sufficient amount so as to obtain a stable, high S/N ratio. For this purpose, when the driving current of, e.g., the LED is increased to increase the light amount, the wavelength of light changes due to heat generated by the LED itself, and the current changes due to changes in forward voltage. As a consequence, a stable light amount cannot be obtained.
Conventionally, a note or notebook type personal computer which comprises a printer unit and a scanner unit attached to the printer unit is commercially available. However, it has been desired to simplify the scanner circuit to attain a size reduction of the computer housing.
Furthermore, in a note personal computer that can be driven by a secondary battery, the consumption power is required to be reduced as much as possible.
It is an object of the present invention to provide an image reading system that can read an image with high image quality.
It is another object of the present invention to provide a compact, energy-saving image reading system.
It is still another object of the present invention to provide an image reading system which can stabilize the illumination characteristics of a light source.
In order to achieve the above object, according an embodiment of the present invention, an image reading apparatus comprises reading means for reading an original, a light source for illuminating the original, power supply means for supplying electric power to the light source, and control means for controlling the power supply means to supply electric power different in quantity from that required upon reading to the light source while the reading means does not read the original.
Furthermore, according to another embodiment of the present invention, a control apparatus comprises power supply means for supplying electric power to a light source of an image reading apparatus having reading means for reading an original and a light source for illuminating the original, and control means for controlling the power supply means to supply electric power different in quantity from that required upon reading to the light source while the reading means does not read the original.
With the above arrangement, high-quality image reading can be attained without wasting consumption power. Also, the illumination characteristics of the light source can be stabilized.